This invention concerns the solution mining os uranium with novel lixiviant. The novel lixiviant is magnesium bicarbonate formed by combining carbon dioxide with magnesium oxide and water.
In known processes for leaching uranium values from underground formations in situ, an oxygenated aqueous solution of an alkaline or acid leaching agent is delivered to the uranium-bearing formation through one or more injection wells. Conventional alkaline leaching agents are sodium, potassium and ammonium carbonates and bicarbonates. The acid or alkaline leaching solution utilized in conjunction with the oxidant transforms the uranium mineral deposit into a soluble salt. The uranium mineral is leached from the formation, dissolved in the leaching solution and subsequently produced from an offsetting production well. The production fluid is then processed for the extraction of the uranium therefrom, with the spent leaching solution and oxidant being either reconstituted for reinjection into the formation or discarded.
Acid and alkaline leaching solutions, and sodium, potassium and ammonium carbonates or bicarbonates present distinct problems. Sodium and potassium cause clay swelling thereby affecting formation permeability and solution sweep efficiencies. Similar undesirable effects arise when sodium and potassium carbonate or bicarbonate cause calcite and gypsum precipitation. Acid leach solutions cause gypsum formation. Acid solutions react with certain formation minerals. Ammonium ions can cause adverse environmental effects which render it necessary to remove the ammonium ions after leaching. Alkaline solutions precipitate alkaline metal from the leach solution causing a decrease in injectivity, permeability and sweep efficiency. Continued injection of sodium, potassium and ammonium carbonates ot their respective bicarbonates in conjunction with oxidants results in a build up of these alkaline metal ions which aggrevates the forming of undesirable precipitates.
In the improved uranium leaching process of this invention, most of the problems associated with sodium, potassium and ammonium carbonates and bicarbonates are overcome or substantially reduced.